This invention relates to a sand filter for use in an oil and/or gas producing well. Oil and/or gas wells are drilled from the earth's surface, the well borehole penetrating into a subterranean hydrocarbon producing formation. Such formations are typically made up of porous rock. That is, oil and/or gas does not occur normally in the manner contemplated by the general public, that is, in pools of liquid or caverns filled with gas. Instead, hydrocarbons are typically found in a rock strata that has porosity and permeability sufficient that entrapped oil and/or gas can flow through the formation. As the porosity of a rock formation increases, the quantity of oil and/or gas in proportion to the mass of the rock can also increase. Further, as the permeability of a rock formation increases, the more freely oil and/or gas can flow from the formation.
Since porosity and permeability are inherent characteristics of most oil and/or gas producing formations, it is inevitable that sand components are typically carried along by the flowing hydrocarbon product.
When substantial quantities of sand are carried along as oil and/or gas is removed from a formation, the sand can eventually plug the openings into the interior of tubing by which the hydrocarbon production is withdrawn to the earth's surface.
When an oil producing well must be pumped, the entrance of sand into the fluid being pumped causes a high rate of pump wear. For these and other reasons, it is important to prevent as much sand as possible from entering into production tubing in a well and, for this purpose, sand filters have long been employed in the petroleum industry.
For information about sand filters and their application in oil or gas wells, see the following U.S. Pat. Nos. 1,367,406; 4,649,996; 1,992,718; 2,342,913; 2,985,241; 2,877,852; 2,858,894; 3,327,865; 4,064,938, 4,317,023; 4,388,968; 4,406,326; 4,428,431; 4,495,073; 4,494,603; 4,526,230; 4,649,996; 4,681,161; 4,811,790 and 4,821,800.
Some filtration systems include the use of packing material, and for reference to these type of filters see U.S. Pat. Nos. 5,082,052; 5,115,864 and 5,232,048.
Sand filters previously used in the petroleum industry have been deficient in several ways. In one way, many of the materials used for providing sand filtration do not possess the required ability to screen out small sand particles, that is, the screening materials let small diameter sand through that can ultimately cause blockage of flow paths or high pump wear. A second problem is that they have relatively small external surface areas so that sand builds up, blocking further flow. It is apparent that longer filter life can be achieved in direct relationship to the external surface area of the filter. Materials that have been used in previous type sand filters do not lend themselves to designing a sand filter in a way to increase the external surface area. A third problem is that many materials that are used for filtration are not capable of withstanding the harsh environment of a producing well. A fourth problem with some type filters is that they are expensive to manufacture and difficult to install.
Therefore, one object of the present invention is to provide an improved sand filtration system for use in oil and/or gas wells that provides improved filtration effectiveness. Another object is to provide a filter that has increased surface area per unit length. Another object is formed of materials capable of withstanding the riggers to which downhole sand filters are subjected and that can withstand the process of positioning them into the bottom of a borehole. In addition, this disclosure provides a sand filtration system that can be expeditiously applied to the exterior of a length of perforated tubing.